The green high-viscosity asphalt modifier used in this study was a self-developed environmentally friendly modification material. The modifier was prepared through a two-step method: first, nano-organic montmorillonite, waste rubber-plastic mixture, and aromatic oil were sequentially fed into a twin-screw extruder at a ratio of 1:4:1, melt-mixed and extruded, then pelletized to produce master batch with particle size of 10–15 mesh; then this master batch was mixed with waste rubber mixture and aromatic oil at a ratio of 1:9:1 and fed again into the twin-screw extruder for secondary melt mixing and extrusion to produce the final product. During processing, the extruder temperature distribution was: feeding section 170°C, seven middle sections all at 175°C, discharge section 170°C, screw speed 120 r/min, pelletizer speed 200 r/min, ensuring sufficient mixing and uniformity of materials. The basic performance indicators of different oil source base asphalts are shown in Table 1.

Using SBS modified asphalt (PG76-22) as the control group, three chemically toughened high-performance asphalts (HP-A, HP-B, HP-C) were prepared by incorporating a green high-viscosity modifier into the respective base asphalts (Wang et al., 2020; Zhang D. et al., 2018). The preparation procedure was as follows: The base asphalts were first heated in an oven at 135°C for 40 min to achieve complete softening, then transferred to an electromagnetic heating vessel. Subsequently, 6% (by weight) green high-viscosity modifier was added to the heated asphalt at 180°C, followed by 15 min of manual preliminary mixing. The mixture was then subjected to high-speed shearing (5,000 rpm, 30 min at 180°C) to ensure thorough dispersion, followed by low-speed mixing (300 rpm, 15 min at 180°C) to achieve homogeneous distribution of the modifier. Finally, the modified asphalt was developed in a sealed oven at 180°C for 70 min to ensure stable modification effects and complete chemical interaction.

To comprehensively simulate asphalt aging behavior under actual service conditions, both short-term and long-term aging tests were conducted on the four asphalt samples (Chen et al., 2021; Zhang H. et al., 2018). Short-term aging was performed using the thin film oven test (TFOT) following the procedure specified in Test Methods of Asphalt and Asphalt Mixtures for Highway Engineering (JTG E20-2011) T0609, where samples were aged at 163°C for 5 h to simulate the aging that occurs during hot mix asphalt production and construction. Long-term aging was conducted using the pressure aging vessel test (PAV) in accordance with JTG E20-2011 T0630, where TFOT-aged samples were further aged at 100°C under 2.1 MPa pressure for 20 h to simulate the oxidative aging experienced by asphalt pavements during extended service life.

The physical properties of chemically toughened high-performance asphalts from different oil sources were evaluated using softening point and Brookfield viscosity as key performance indicators (Han et al., 2020; Tan et al., 2012). The softening point was determined using the ring-and-ball method in accordance with JTG E20-2011 T0606. Brookfield viscosity measurements were performed following JTG E20-2011 T0625 using a No. 21 spindle at a rotation speed of 20 rpm, with torque maintained within the range of 10%–98% and test temperature controlled at 80°C.

According to JTG E20-2011 T0628, dynamic shear rheometer (DSR) was used to determine asphalt complex modulus (G*) and phase angle δ and calculate rutting factor (G*/sinδ) (Tan et al., 2020; Vestena et al., 2021). Test conditions were: temperature range 46°C∼88°C, 6°C intervals, temperature sweep plate diameter 25 mm, gap 1 mm.

Fourier transform infrared spectroscopy (FT-IR) was employed to analyze the chemical structure of asphalt at the molecular level (Zhu et al., 2018; Zhang S. et al., 2021). The technique was used to identify functional group positions and monitor intensity variations in characteristic peaks, with particular focus on the formation and transformation of oxygen-containing functional groups such as carbonyl and sulfoxide groups. Spectral data were collected using a resolution of 4 cm⁻¹ over the wavenumber range of 400–4,000 cm⁻¹ with 64 scans per measurement.

The compatibility between asphalts from different oil sources and green high-viscosity modifiers is a critical factor determining the performance of modified asphalt (Xing et al., 2020; Wang et al., 2020). Figure 1 presents a comparative analysis of softening point and Brookfield viscosity for four modified asphalts.

HP-C asphalt demonstrated exceptional dual-high performance characteristics, achieving a softening point of 78.2°C and Brookfield viscosity of 4.85 Pa·s—representing increases of 17.8% and 32.4%, respectively, compared to SBS asphalt. This superior compatibility stems from the unique colloidal structure of BA-C asphalt, where moderate asphaltene content and high resin content provide an optimal swelling medium for rubber molecules, facilitating the formation of robust physical-chemical synergistic networks (Zhu et al., 2019; Zhang D. et al., 2018).

In comparison, HP-A asphalt exhibited moderate performance with a softening point of 72.1°C and Brookfield viscosity of 3.42 Pa·s. This intermediate performance is attributed to the relatively high saturate content in BA-A asphalt, which, while promoting modifier dispersion, contributes limitedly to high-strength crosslinked network formation (Chen et al., 2022; Duan et al., 2023). SBS asphalt displayed a double-valley phenomenon, indicating compatibility challenges between the green high-viscosity modifier and existing SBS polymer networks, likely due to competitive crosslinking reactions that compromise overall modification effectiveness.

From a molecular perspective, the high aromatic content (∼41.2%) in BA-C asphalt creates an ideal intercalation environment for nano-montmorillonite within the modifier. The π-π interactions between aromatic ring structures and rubber molecular chains significantly enhance interfacial bonding strength (Caputo et al., 2020; Zhang S. et al., 2021). This molecular-level synergistic mechanism underlies the exceptional compatibility observed in HP-C asphalt.

Figure 2 illustrates the temperature-dependent rutting factor behavior of four asphalts. All asphalts exhibited decreasing rutting factors with increasing temperature, consistent with fundamental rheological principles, though distinct performance differences were evident among the samples (Tan et al., 2020; Li et al., 2021).

At low temperature (46°C), HP-C asphalt demonstrated superior performance with a rutting factor of 121.24 kPa, significantly exceeding the other three asphalts and indicating exceptional resistance to permanent deformation under high-temperature loading conditions. As temperature increased, the performance gap among asphalts gradually narrowed, yet distinct behavioral patterns emerged: HP-A asphalt maintained the lowest rutting factor below 72°C, while above this threshold, SBS asphalt exhibited the most pronounced decline, reaching only 0.791 kPa at 88°C.

This complex temperature-dependent behavior can be attributed to several underlying mechanisms. HP-C asphalt, enriched with asphaltenes and resins, forms stable crosslinked networks with modifiers (Zhang H. et al., 2018), providing robust initial resistance to shear deformation. Conversely, as temperature rises, the styrene-butadiene-styrene triblock copolymer networks in SBS asphalt become increasingly active, enhancing molecular chain flexibility and paradoxically improving high-temperature stability (Wang et al., 2020). HP-A asphalt, potentially containing higher concentrations of low molecular weight components, becomes more susceptible to thermal softening, resulting in rapid deterioration of deformation resistance. These findings further validate the superior compatibility between green high-viscosity modifiers and HP-C asphalt, particularly in enhancing high-temperature performance stability.

Figure 3 demonstrates that all four asphalt samples exhibited minimal softening point differences, with a maximum variation of only 2.15°C. Importantly, all three modified asphalts satisfied the regulatory upper limit of 2.5°C, indicating acceptable storage stability (Han et al., 2019; Lesueur et al., 2013). HP-C asphalt demonstrated superior storage stability with the smallest softening point difference (1.3°C), followed by HP-B asphalt (1.65°C). SBS modified asphalt (1.8°C) and HP-A asphalt (2.15°C) showed comparatively higher variations, though still within acceptable limits. These performance differences primarily reflect varying compatibility between base asphalts and modifiers (Chen et al., 2021). The pre-existing stable polymer network structure in SBS asphalt facilitates synergistic interactions with green high-viscosity modifiers, enhancing mixture homogeneity. Similarly, the high aromatic content in HP-C asphalt promotes favorable compatibility with rubber components in the modifiers. Conversely, the elevated saturated hydrocarbon content in HP-A asphalt reduces modifier affinity, potentially leading to localized phase separation. Despite these variations, all four asphalts met engineering application standards for storage stability, demonstrating the excellent universality of green high-viscosity modifiers and their ability to form stable composite systems across different oil source asphalts.

Softening point increment serves as a sensitive indicator of molecular structure changes in asphalt (Zhang D. et al., 2018; Chen et al., 2021). Table 2 and Figure 4 reveal distinct hardening patterns among different modified asphalts during aging. During short-term aging, HP-A asphalt exhibited the minimal softening point increment (0.4°C), attributed to its unique compositional characteristics. The high resin content in BA-A asphalt primarily undergoes light component volatilization under TFOT conditions, with minimal changes in intermolecular association, resulting in limited hardening effects.

In contrast, HP-C asphalt demonstrated a substantial softening point increment of 6.0°C during short-term aging, indicating pronounced oxidation reactions at 163°C. The high aromatic content in BA-C asphalt readily forms condensed aromatic hydrocarbons and quinone compounds under high-temperature oxidative conditions, intensifying intermolecular π-π interactions and manifesting macroscopically as significant softening point elevation.

Long-term aging revealed a reversed performance pattern. HP-C asphalt showed only a 4.2°C softening point increment, substantially lower than HP-A asphalt’s 10.1°C increase. This performance reversal reflects fundamentally different aging mechanisms: under prolonged aging conditions, resin components in HP-A asphalt undergo extensive oxidation, generating substantial asphaltenes and causing dramatic molecular weight increases. Conversely, HP-C asphalt benefits from the natural antioxidant properties of aromatics, resulting in slower oxidation rates, while antioxidant components in the modifiers provide synergistic protection (Zhang S. et al., 2021).

The viscosity aging index provides a direct measure of asphalt flow property deterioration during aging (Zhang H. et al., 2018; Amini and Hayati, 2020). Data presented in Figure 5 and Table 3 demonstrate that SBS asphalt exhibited the most severe viscosity increase, with an aging index reaching 103.8% after long-term aging. This dramatic deterioration results from thermally-induced crosslinking of SBS polymer chains under prolonged oxidative conditions, forming high-molecular-weight three-dimensional gel networks that substantially increase system viscosity and compromise flow characteristics.

HP-C asphalt demonstrated superior aging resistance, maintaining the lowest viscosity aging indices throughout the aging process at 2.6% and 6.1% for short-term and long-term aging, respectively. This exceptional anti-aging performance stems from synergistic protection mechanisms operating at multiple levels (Zhang S. et al., 2021; Xu et al., 2022): the abundant aromatic compounds in BA-C asphalt function as natural radical scavengers, effectively terminating oxidative chain reactions; nano-montmorillonite platelets within the modifier create physical barrier networks that restrict oxygen diffusion into the asphalt matrix; additionally, carbon black and other particulate fillers from recycled rubber provide UV radiation shielding, further retarding photo-oxidative degradation processes.

HP-B asphalt exhibited intermediate aging behavior with viscosity aging indices of 3.9% and 8.6% for short-term and long-term aging, respectively. The moderate resin content in BA-B asphalt leads to formation of intermediate-molecular-weight oxidation products during aging, primarily consisting of resin-asphaltene associates that exert comparatively mild effects on bulk viscosity properties. This intermediate performance reflects the balanced compositional characteristics of BA-B asphalt, which provides reasonable aging resistance without the enhanced protection mechanisms present in HP-C systems.

Figure 7 illustrates the temperature-dependent rutting factor evolution of four modified asphalts across different aging stages (Li et al., 2021; Tan et al., 2020). Aging processes substantially alter asphalt rheological properties, with all samples exhibiting varying degrees of rutting factor enhancement, though through fundamentally different mechanisms. HP-C asphalt demonstrated pronounced rutting factor increases following short-term aging, rising from 45.3 kPa to 67.8 kPa at 64°C—representing a 49.7% enhancement. This improvement stems from oxidative formation of polar functional groups (carbonyls, sulfoxides) that strengthen intermolecular associations and enhance the material’s elastic modulus (Zhang H. et al., 2018). After long-term aging, the rutting factor further increased to 78.2 kPa, though at a reduced rate (15.3%), suggesting that oxidative reactions approach thermodynamic equilibrium under prolonged exposure.

SBS asphalt exhibited distinctly different aging characteristics (Wang et al., 2021). Following short-term aging, significant rutting factor increases occurred in the low-temperature regime, while high-temperature performance improvements remained modest. This selective enhancement reflects the sequential oxidation of SBS molecular architecture: preferential oxidation of butadiene segment double bonds initially generates crosslinking sites that enhance low-temperature elastic recovery, while thermal softening of styrene hard domains continues to dominate high-temperature response, limiting overall high-temperature performance gains.

HP-A asphalt displayed unique initial behavior, with rutting factors actually decreasing during early short-term aging—a phenomenon attributed to temporary softening caused by rapid volatilization of maltene fractions. As aging progressed, the accumulation of oxidative products (primarily asphaltenes formed from resin oxidation) gradually restored and eventually elevated rutting factors above unaged baseline levels. This biphasic response reflects the competing effects of volatile loss versus oxidative hardening that characterize HP-A asphalt’s aging progression.

The sulfoxide aging index results presented in Figure 8 provide critical insights into sulfur compound oxidation pathways within asphalt matrices. Sulfoxide groups (S=O) represent key intermediate products in the oxidative transformation of sulfur-containing compounds, with their concentration changes serving as reliable indicators of oxidative degradation in sulfur-bearing asphalt constituents (Duan et al., 2025). HP-B asphalt exhibited the most pronounced sulfoxide aging index increase at 29.28%, substantially exceeding other samples. This elevated oxidative susceptibility directly correlates with the inherently high sulfur content characteristic of BA-B crude oil source, providing abundant reactive substrates for oxidative transformation.

HP-A asphalt demonstrated a more moderate sulfoxide increase of 22.78%, consistent with its relatively lower sulfur content profile. SBS asphalt presented the most dramatic sulfoxide accumulation, reaching 57.41%, attributed to the oxidative degradation mechanisms specific to styrene-butadiene-styrene copolymers. The preferential oxidative cleavage of unsaturated butadiene segments generates sulfur-containing radical species that accelerate sulfoxide formation, while the comparative thermal stability of styrene domains provides only partial mitigation of this oxidative cascade.

HP-C asphalt demonstrated superior oxidative stability with the minimal sulfoxide aging index increase of only 18.5%, further validating its exceptional anti-aging characteristics. The abundant phenolic and aromatic compounds inherent in BA-C asphalt function as effective radical scavengers, intercepting sulfur-derived free radicals generated during oxidative processes and effectively terminating propagating chain reactions. This natural antioxidant network provides comprehensive protection against sulfur compound oxidation, maintaining chemical stability throughout extended aging exposure.